An image forming apparatus is available as various types of apparatuses such as printer, facsimile apparatus, copier, plotter, and multifunctional apparatus (having printer/facsimile/copier functions), for example.
Such image forming apparatus may include a carriage having a recording head (or printing head), which can discharge droplets of recording liquid (e.g., ink).
Such carriage may be moved in a direction perpendicular to a transport direction of a recording medium in the image forming apparatus, for example. The recording medium includes a recording sheet, a transfer member, for example, wherein the recording sheet and transfer member includes a paper sheet.
Such recording medium may be transported intermittently into a sheet transport direction to record images on the recording medium. With such process, images can be formed or printed on the recording medium.
Such process can be conducted by an image forming apparatus of serial type, and an image forming apparatus having line type having line head. In the serial type, a recording head (e.g., inkjet head) may be moved in a given direction over a recording medium. In the line type, a recording medium may be moved in a given direction under a recording head (e.g., inkjet head), for example.
Such image forming apparatus may conduct gray-scale printing as mentioned below, for example.
A reference drive pulse pattern having a plurality of drive signals (or drive pulses) is generated for one-dot print cycle (or one-drive period). Then, one drive signal or some drive signals are selected from the reference drive pulse pattern.
Such selected signals can be transmitted to a pressure-generating device (e.g., actuator), which generates energy for discharging droplets from the recording head.
Based on the selected signals, the recording head may discharge droplets having a same droplet size or droplets having different droplet sizes, and such droplets may be impacted on a same impact position on a recording medium to form dots having different sizes.
In one background image forming apparatus, a plurality of discharge drive pulses for discharging droplets and a non-discharge drive pulse for vibrating a meniscus slightly (i.e., droplet is not discharged) are included for a drive pulse pattern used for one-dot print cycle (or one-drive period), wherein the plurality of discharge drive pulses may be output sequentially.
Such drive pulses may include a first signal for increasing a volume capacity of a pressure-generating room, a second signal for maintaining the increased volume capacity of the pressure-generating room after the first signal, and a third signal for contracting the volume capacity of the pressure-generating room after the second signal.
Another background image forming apparatus includes a drive signal generator, which generates a reference drive signal for bi-directional printing, in which a printing operation is conducted in one direction, and then a next printing operation is conducted in opposite direction.
The reference drive signal may include a first pulse and a second pulse generated sequentially. The first pulse may be used for discharging a liquid droplet at a relatively slower speed, and the second pulse may be used for discharging a liquid droplet at a relatively faster speed.
Further, a related art image forming apparatus may include a drive signal generating circuit and a recording head.
When the recording head is moved in a first direction for one printing operation, the drive signal generating circuit generates a first-type drive signal which may generate a discharge pulse for a medium-sized dot and a discharge pulse for a smaller dot, in this order.
When the recording head is moved in a second direction, opposite to the first direction, for a next printing operation, the drive signal generating circuit may generate a second-type drive signal which generates the discharge pulse for the medium-sized dot, for the smaller dot and the discharge pulse in this order, in which the drive signal generating circuit generates a minute-vibrate pulse between the smaller dot discharge pulse and medium-sized dot discharge pulse. The minute-vibrate pulse is supplied to a pressure generating element by a pulse supplying device before the medium-sized dot discharge pulse is generated after the smaller dot discharge pulse.
In general, an improvement such as concurrent improvement of high-speed printing and higher image quality may be demanded on an image forming apparatus.
In order to achieve such improvement on printing speed, a plurality of types of droplets may be discharged from the same nozzle, wherein the plurality of types of droplets use different amounts of recording liquid (e.g., ink). Specifically, a drive pulse pattern having a plurality of drive signals may be generated for one-dot print cycle (or one-drive period), and the drive signals selectively applied to form different sized dots such as smaller to larger dots.
It is preferable to shorten the one-dot print cycle (or one-drive period) to improve a printing speed to a higher speed.
However, if the one-dot print cycle (or one-drive period) is shortened, numbers of drive signals to be included in a drive pulse pattern may become smaller, by which it may become difficult to discharge a various types of droplets in one-dot print cycle (or one-drive period).
Further, in order to realize a higher image quality, it is preferable to merge a plurality of droplets as one droplet when the droplets are traveling through the air and to impact the one droplet to the recording medium compared to impacting a plurality of droplets on a same impact position on the recording medium, one by one.
Accordingly, in order to achieve high-speed printing and higher image quality concurrently, there is a need for improvement of drive pulse pattern and improvement of precision of impact position on the recording medium by a plurality of droplets.
In the above-mentioned another background image forming apparatus, a discharge speed of droplet by the first drive pulse is set to be relatively slower, and a discharge speed of droplet by a second drive pulse is set to be relatively faster, wherein the first drive pulse is applied before the second drive pulse.
With such speed adjustment for droplet, a discharge speed of droplet can be set greater for a later-discharged droplet than an earlier-discharged droplet so that the earlier-discharged droplet and the later-discharged droplet can impact on the same impact position on a recording medium.
However, if a larger droplet is to be discharged by one drive signal, a droplet amount that can be discharged by the one drive signal may have a limitation.
Further, when a larger dot is formed with a plurality of drive signals, an image quality may degrade because such plurality of droplets may be impacted on a recording medium one by one to form one dot.
Further, in the above-mentioned related art image forming apparatus, different drive signals may be required for conducting a printing operation in the first and second direction, which is opposite each other. Further, a higher image quality may not be obtained for a larger dot because the smaller dot and medium-sized dot may impact on different positions when forming the larger dot on the recording medium.